Pumping of two phase fluid mixtures of liquid and gas such as foams, froths, and bubbly liquids, is much more difficult than the pumping of single phase fluids such as gas or liquid. Two phase fluids such as those enumerated exhibit properties which change rapidly according to the void fraction occupied by the gaseous phase. Moreover, it is extremely difficult to maintain a homogeneous mixture of the two phases in conventional pumps. Changes in the void fraction result from segregation of the various fluids by reason of the action of inertia forces, gravity or shear forces and are generally unavoidable in almost any application. They are also induced by pressure changes or slips between the velocities of the two phases that are attempted to be pumped. In any event, the net effect is that the actual properties of the mixture at any point inside the pump are poorly known with the ultimate result that it is difficult to design the pump geometry to handle the fluid because of its uncertain properties.
Consequently, in many instances, the pump performance simply breaks down when the void fraction reaches a certain level and fluid delivery ceases altogether. Continued operation of the pump results in high vibration and noise levels.
To avoid these difficulties, the prior art has generally attempted to try to maintain the state of the two phase mixture in a homogenous form in which the gas content is uniformly and finely dispersed throughout the liquid as uniformly as possible. Typically, this is attempted to be achieved by inducing high levels of turbulence. In other attempts at solution of the problem, separation of the phases has been attempted with independent and separate pumping devices for each phase. Frequently these methods are capable of producing some degree of improvement but often they work with one type of mixture and not with another.
The present invention is directed to overcoming one or more of the above problems.